In a speech at the GDST's annual conference, Ms Fraser also argued that being at a single-sex school can help teach young women how to get on in their careers.

She told delegates that she has worried about why high-achieving teenage girls do not climb as easily up the career ladder as their male peers.

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Ms Fraser argued that one way to build girls' confidence is to coax them away from "perfect good girl behaviours", allowing them to take risks in the classroom and on the sports field, and to stand out and be heard.

"We want our schools to take girls away from being quiet, neat, 'good girls' to becoming adventurous risk takers who don't allow their inner critic to silence their voices," she said.

"We need to persuade girls to challenge that inner critic that judges you, tells you you're not good enough, that your ideas aren't worth hearing. We know that too many girls and women, especially in a situation they find slightly intimidating (a university interview for example, or being the only woman sitting on a board), allow their inner critic to prevent them from speaking up or speaking out.

This silencing of girls' voices leads to a sort of self-censorship. If you don't have that confidence in your own abilities, you can talk yourself out of expressing an opinion before you even open your mouthHelen Fraser, GDST

"This silencing of girls' voices leads to a sort of self-censorship. If you don't have that confidence in your own abilities, you can talk yourself out of expressing an opinion before you even open your mouth. And if the female half of the population are routinely censoring themselves, their great ideas aren't getting aired and implemented and the world is a poorer place."

She added: "Our girls, I believe, learn to challenge that inner critic with their inner cheerleader, and this means, throughout their lives, they can do, achieve and enjoy more."